The objective of this proposal is to investigate quantitatively the effects of early abnormal visual experience, leading to amblyopia, on the human accommodation system, with primary emphasis on target contrast and spatial frequency component contributions. Subjects having functional amblyopia will be the primary target population; matched controls will include visually-normal individuals as well as strabismics without amblyopia. Four sets of experiments will be conducted: (1) accommodation will be monitored continuously and objectively using an infrared optometer, and the average accommodative response level will be determined using a computer averaging program, as either the amblyopic or fellow dominant eye views and focuses on a sinusoidal grating at a variety of contrast (80 to nearly 0%)/spatial frequency (0.5, 4.0, or 16.0 cycles per deg.) combinations; (2) accommodation will be monitored continuously and objectively using an infrared optometer, and the average accommodative response level will be determined using a computer averaging program, as either the amblyopic or fellow dominant eye views and focuses on either a high contrast square-wave grating, a high contrast sine-wave grating having the same fundamental frequency, or the fundamental sine-wave grating with addition of increasingly higher-order (3rd, 5th, and 7th), odd harmonic sinusoidal components; (3) contrast discrimination will be investigated, using a forced-choice design and statistical techniques, by having the subject judge whether the contrast of a flashed sinusoidal test grating is the same or different than a flashed sinusiodal reference grating; discrimination will be tested for sevral contrast/spatial frequency combination will be followed during the course of orthoptic therapy for the amblyopia, using the stimuli and methods described in experiments 1 - 3 above.